1. Field of the Invention
The present invention relates to a battery including a battery element in which a cathode and an anode are layered with a separator in between.
2. Description of the Related Art
In recent years, many portable electronic devices such as a combination camera (videotape recorder), a mobile phone, and a notebook personal computer have been introduced, and downsizing and weight saving of such devices have been made. Research and development for improving the energy density of the battery used as a portable power source for such electronic devices, in particular the secondary battery as a key device has been actively promoted. Specially, a nonaqueous electrolyte secondary battery (for example, lithium ion secondary battery) provides a higher energy density compared to a lead battery or a nickel cadmium battery that is an existing aqueous electrolytic solution secondary battery. Therefore, improvement thereof has been considered in respective fields.
For such a secondary battery, improving the energy density associated with miniaturization of an electronic device or the like on which the secondary battery is mounted and improving safety have been strongly demanded. Thus, suggestions about how to improve safety of the secondary battery have been made by approaches from various viewpoints. For example, in Japanese Unexamined Patent Application Publication No. 2005-228537, the width of a current collector in an electrode in a region not covered with an active material layer (exposed region) is narrower than that in a region covered with the active material layer. Thereby, movement (uneven distribution) of an electrolytic solution component is inhibited, and short circuit generated due to collapse of spirally winding state of the battery element is prevented. Further, in Japanese Unexamined Patent Application Publication No. 2008-34353, anode size to a cathode is optimized in a state that a battery is charged. Thereby, lithium ions are reduced in a region other than an anode active material layer, resulting in preventing lowered discharge capacity, short circuit or the like.